The Tissue Level of Organization

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The Tissue Level of Organization
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Tissue

• Definition a group of cells that are
• (1) similar
• (2) have a common embryological origin, and
• (3) carry out a specialized activity.
• Histology is the science that studies tissue.
• Pathology is the study of the effects of disease
  on cells and tissues.

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Types of tissue

• Epithelial tissue covers the body surface, hollow
  organs, lines body cavities, and forms glands.
• Connective tissue protects and supports the body
  and its organs. It stores energy reserves as fat
  and provides immunity against disease causing
  organisms.
• Muscular tissue generates the physical force
  needed to move the body.
• Nervous tissue detects changes inside and outside
  the body and regulates responses through
  electrical and chemical signals.

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The origins of different tissues

• Epithelial tissue comes from all germ layers.
• Connective and most muscle tissue comes from
  mesoderm.
• Nervous tissue comes from ectoderm

• Three germ layers
• Ectoderm
• Mesoderm
• Endoderm

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Cell junctions
Adherens junctions Found in intestine

• Tight junctions
• Found in lining of stomach, intestine, and bladder

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Cell junctions
Hemidesmosomes

• Desmosomes
• Found in the epidermis
• Cardiac muscle cells

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Cell junctions

• Gap junctions
• Found in muscle and nerve cells
• Is used for cellular communication and NOT to
  attach cells to one another.

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Characteristics of epithelial tissue

• Polarity
• Specialized contacts
• Supported by connective tissue
• Avascular but innervated
• Capable of regeneration

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Epithelial tissue

• Consists of cells arranged in continuous sheets
  in single or multiple layers.
• Epithelial cell surfaces
• Apical surface faces body surface, body cavity,
  lumen of an organ or tubular duct
• Lateral surface faces adjacent cells.
• Basal surface is opposite the apical surface and
  attaches to the basement membrane.
• Basement membrane is made up of the basal lamina
  secreted by the epithelial cell and the reticular
  lamina which is next to the underlying connective
  tissue and produced by fibroblasts.

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Epithelial cell surfaces
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Covering and lining epithelium

• Arrangement of cells in layers
• Simple epithelium is a single layer
• Pseudostratified epithelium is simple epithelium
  that appears as multiple layers
• Stratified epithelium has two or more layers of
  cells.

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Covering and lining epithelium

• Cell shapes
• Squamous cells are like floor tiles
• Cuboidal cells are shaped like cubes or hexagons
  and may have microvilli.
• Columnar cells are taller than they are wide.
  Their apical surface may have microvilli or
  cilia.
• Transitional cells change shape from flat to
  cuboidal.

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Functions of epithelial cells

• Simple and pseudostratified epithelium function
  in diffusion, osmosis, filtration, secretion, and
  adsorption.
• Stratified epithelium are used to protect
  underlying tissue.
• Squamous cells allow for rapid passage of
  substances
• Cuboidal and columnar cells function in secretion
  or absorption.
• Transitional cells provide the ability to
  stretch.

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Class discussion

• Which cells share the same function? Do you
  think the structure of the cell dictates the
  cells function?
• Epithelial tissue is found in many places. What
  do these places have in common? Are secreting
  epithelial cells found in particular places? Are
  diffusing epithelial cells found in different
  places? Are stratified epithelial cells found in
  particular places?

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Papanicolaou (Pap) Test

• The collection of epithelial cells from the
  apical layer of tissue.
• Common Pap test is from the stratified cells of
  the vagina or cervix to detect precancerous
  changes in cells.

High-grade squamous intraepithelial lesion
(Bethesda system). A shows moderate to severe
dysplasia, Papanicolaou smear, and B shows
corresponding histology of severe
dysplasia/carcinoma in situ (CIN III)
(hematoxylin-eosin, X200). Images courtesy of N.
N. Ku, MD, Pathology Service, H. Lee Moffitt
Cancer Center Research Institute.
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Glandular epithelium

• A gland secretes substances into a duct, on a
  surface, or into the blood.
• Endocrine glands secrete into interstitial fluid
  which diffuses into the blood stream.

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Glandular epithelium

• A gland secretes substances into a duct, on a
  surface, or into the blood.
• Exocrine glands secrete into ducts that empty
  onto the surface of a covering or lining
  epithelium.

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Structural classification of exocrine glands

• Unicellular glands are single celled.
• Example is globlet glands that secrete mucous
• Multicellular gland categories
• Unbranched ducts or simple
• Branched ducts or compound
• The shape of the secretory portion of the glands.
• Glands with tubular secretory parts are tubular
• Glands with rounded secretory parts are acinar
• Glands with both features are tubuloacinar

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Structural classification of exocrine glands
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Functional classification of exocrine glands

• Merocrine glands use secretions that are
  synthesized on ribosomes on rough ER processed,
  sorted, and packaged by the Golgi complex and
  released by the cell in secretory vesicles.

Example salivary glands, pancreas
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Functional classification of exocrine glands

• Apocrine glands accumulate their secretory
  products in the apical surface of the secreting
  cell and that portion is pinched off to release
  the secretion.

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Functional classification of exocrine glands

• Holocrine glands accumulate a secretory product
  in their cytosol. The cell matures and ruptures,
  releasing the secretory product.

Example sebaceous gland
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Connective tissue characteristics

• All connective tissue arises from mesenchyme.
• Made up of two basic elements
• Cells
• Extracellular matrix
• Material (usually protein fiber and ground
  substance) located between cells
• Secreted by connective tissue cells
• Does not occur on the body surface.
• Has variable degrees of blood supply
• cartilage and dense regular (tendons) have none
• Has nervous input
• Is comprised mostly of the non-living
  extracellular matrix.

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Connective tissue cells

• The immature cells of connective tissue are
  -blast cells. They secrete the extracellular
  matrix
• Fibroblasts are in loose and dense connective
  tissue
• Chondroblasts are found in cartilage
• Osteoblasts are found in bone
• The mature cells are cyte cells and have a
  reduced capacity for cell division. They
  maintain the cell matrix

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Connective tissue cells
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Ground tissue extracellular matrix

• Ground substance is found in between cells and
  fibers.
• Composed of
• Water
• Polysaccharides
• Chondroitin sulfate--cartilage, bone, skin, and
  blood vessels
• Dermatan sulfateskin, tendons, blood vessels,
  heart valves
• Keratan sulfatebone, cartilage, cornea
• Hyaluronic acid (hyaluronidase),
• Glycosaminoglycans (GAGs) polysaccharides that
  form a complex with proteoglycans
• Adhesion proteins (fibronectin) that link the
  ground substance to surfaces of cells.

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Ground tissue extracellular matrix

• Ground substance may be fluid, semifluid,
  gelatinous, or calcified.
• Functions
• Tissue development
• Migration
• Proliferation
• Shape change
• Metabolism

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Ground tissue extracellular matrix

• Collagen Fibersstrong and flexible, able to
  resist pulling forces
• Elastic fibersstrong but stretchy fibers that
  can be stretched 150 of relaxed length and
  return to original shape
• Reticular fiberscollagen coated with
  glycoproteins found in connective tissue that
  forms the stroma or supporting framework of soft
  organs

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Membranes

• Epithelial membranes are a combination of an
  epithelial and a connective tissue layer.
• Synovial membranes are composed of a
  discontinuous layer of cells called synoviocytes
  and either areolar or adipose connective tissue.

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Epithelial membranes

• Mucous membranes line body cavities that open to
  the exterior.
• Description made up of simple epithelium and
  lamina propria secreted by fibroblasts.
• Tight junctions join the two layers and prevent
  leakage of fluids.
• Epithelial layer
• Mucous, produced by goblet and other epithelial
  cells, provides a barrier to microbes and
  pathogens.
• Secretes fluids that enhance movement of food
• Secretes digestive enzymes and enhances
  absorption.

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Epithelial membranes

• Mucous membrane
• Lamina propria
• Supports epithelium, binds it to underlying
  structure.
• Allows flexibility of membrane
• Holds blood vessels in place
• Protects underlying muscles from abrasion

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Serous membranes

• Lines body cavities that do not open to the
  exterior.
• Description areolar connective tissue covered
  by mesothelium (simple squamous epithelium).
• Parietal layer attaches to the cavity wall.
• Visceral layer attaches to the organs inside the
  cavity
• The mesothelium secretes serous fluid which
  lubricates the outside of the organs.
• Location Pleura, pericardium, peritoneum

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Serous membranes
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Cutaneous membranes

• Skincovers the surface of the body.
• Epidermis is keratanized stratified squamous
  epithelium
• Dermis is areolar connective tissue and dense
  irregular connective tissue

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Synovial membranes

• Lines the cavities of freely moving joints .
• Synoviocytes secrete synovial fluid

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Muscular tissue

• Skeletal muscle tissue
• Attached to bone
• Has long, cylindrical shape
• Has striations
• Relaxation and contraction under voluntary
  control.
• Multinucleated

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Muscular tissue

• Cardiac muscle tissue
• Forms the wall of the heart
• Has branched striated fibers
• Contractions are involuntary
• Has centrally located nucleus (rarely nuclei)
• Attach end to end through intercalated discs.

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Muscular tissue

• Smooth muscle tissue
• Located in the wall of hollow internal structures
• Has spindle shaped non-striated fibers
• Contractions are involuntary
• Has centrally located nucleus
• Gap junctions connect fibers

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Nervous tissue

• Basic parts of a neuronal cell
• Cell body, which contains the nucleus and
  organelles
• Cell dendrites, which receive input from other
  neurons.
• Cell axon, which conducts electrical impulses to
  other neurons or tissue.
• Neuroglia function as support cells for neurons

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Nervous tissue